In modern surgery, one of the most important instruments available to medical personnel is the powered surgical drill. Typically, this drill comprises a housing in which a motor is secured called a handpiece. The motor has a shaft that is connected to some type of chuck or other coupling assembly that is mounted to the housing. The coupling assembly holds a cutting accessory that is applied to the patient in order to perform a specific medical procedure. Some common cutting accessories are drill bits, burs and reamers. These accessories are used to drill into and/or separate sections of soft tissue and hard tissue, commonly referred to as bone. The ability to use surgical drills to actuate these and other cutting accessories has lessened the physical strain of physicians and other medical personnel that perform these medical procedures. Moreover, most surgical procedures can be performed more quickly and more accurately with powered surgical tools than with the manual equivalents that preceded them.
Surgical drills are often used in certain orthopedic surgical procedures in order to facilitate the repair of fractured and broken bones. These fractures and breaks typically occur as a result of trauma to the bone. In this type of procedure it is common practice to fit a pin or screw to the adjacent sections of the bone so as to hold these sections together. In this type of procedure, the drill is used to form a bore/hole/holes in the section/sections of the bone into which the pin or screw is to be fitted.
In this type of procedure, the drill bit, while it should extend through the bone, should not be pressed to extend beyond the bone. This is because if the tip of the drill bit, presses through the bone, the tip could damage the soft tissue adjacent the opposite side of the bone. This damage is more likely to occur if the tip, when pressed against the soft tissue, is rotating.
Accordingly, when a surgeon is forming a bore in a bone in order to set a pin or a screw, the surgeon must typically use extreme care to ensure that, as soon as possible after the drill bit tip penetrates the bone, the drill is deactivated.
One means suggested to reduce the extent to which a rotating drill bit is allowed to press into soft tissue adjacent a bone is to provide trauma surgeons with drills similar to the cranial perforators used by neurosurgeons. A cranial perforator is a drill used by a neurosurgeon to form the initial entrance opening into the skull. A cranial perforator includes a head and inner and outer drills. The inner drill is in the form of a solid cylinder. The outer drill is in the form of a sleeve that extends circumferentially around the inner drill. Both drill bits extend from the head. The head is attached to handpiece with a motor. Internal to both the head and the drill bits are features that, when engaged, cause the drill bits to rotate with the rotation of the head. Also, internal to the head is a spring. The spring normally holds at least one of the drills away from the complementary features integral with the head. When the drill bits are pressed against bone, the resistance of the bone pushes the drill bit and head features into engagement. When the perforator is in this state, the rotation of the head results in a like rotation of the drills. The rotational moment and forward force of the drills causes the drills to form the desired bore. When at least one of the drills, typically the inner drill, completely penetrates the skull, the skull no longer offers resistance to the release action of the spring. The spring pushes the drills away from the head. Thus, when the perforator is in this state, the rotation of the head does not cause a like rotation of the drills. Since the drills are not rotating when the perforator is in the this state, the pressing of the drills against the tissue, the thin soft tissue below the skull does not result in appreciable damage to this tissue.
One reason cranial perforators work well for forming bores in the skull is that the skull is relatively thin. Typically the skull has a thickness of 1.5 cm or less. Thus, once the bore is formed, the surgeon, with using only a minimal amount of force, can pull the perforator out of the newly formed bore.
In trauma surgeries and other orthopedic surgeries the surgeon may want to form a bore hole in bone that is relatively thick, having a thickness of 3.0 cm or more. Owing to the tight fit of the drill bit in the bore, it is rather difficult to simply pull the bit out of the bone. If a medical practitioner uses a large amount of manual force, there is the possibility that if they use this back force, especially if coupled with a back and forth prying action, can damage the bone.
To avoid the possibility of this post bore formation bone damage, an orthopedic surgeon typically drives the drill bit in reverse in order to facilitate the backing out of the bit from the bore. However, as mentioned above, once the drills of a cranial perforator penetrate the bone, they are disengaged from the complementary head. Driving the head in reverse does not foster a like rotational movement of the drills. This is why cranial perforators, while useful for preventing damage to the tissue underlying the bone against which they are pressed, have not proven particularly suitable for forming the relatively deep bores required by orthopedic surgeons.
Another problem with the use of cranial perforators is that during the formation of a bore, the drill bit may disengage from the motor before the bore is completely formed. The orthopedic surgeon may need to remove the drill and then re-drill the bore again to complete the formation of the bore.
The Inventor's U.S. patent application Ser. No. 13/798,866, filed 13 Mar. 2013, now US Pat. Pub. No. US 2013/0245629 A1, the contents of which are hereby incorporated by reference, discloses a perforator like device for drilling into bone where a clutch mechanism both prevents overdrilling and allows the drill bit to be driven in the reverse direction. A limitation of this device is that it requires a bit assembly that includes inner and outer bits. Many orthopedic surgeons prefer working with a bit assembly that consists of a single drill bit.
An additional issue faced by orthopedic surgeons is that it is difficult and time consuming during surgery to use the current depth gauges to determine the depth of a bone bore. Current depth gauges use a piece of wire with a hook to try and measure the depth of the bore. The wire and hook is placed through the bone bore and moved until the hook catches on the bone adjacent the bottom of the bore. The surgeon places their finger on the wire adjacent the bore and removes the wire from the bore. The distance between the surgeon's finger and the hook represents the depth of the bore.
Unfortunately, if the surgeon's finger is placed incorrectly or slips, the measurement will be incorrect. Also, when the hook extends through the bone bore and out from the bottom of the bore, adjacent tissues can be subject to damage.